53 



V 



Issued May 10, 1917. 

DEPARTMENT OF AGRICULTUEE, 
BUREAU OF ANIMAL INDUSTRY. 

A. D. MELVIN, Chief. 



CHEMICAL TESTING OF MILK 
AND CREAM. 



BY 



ROSCOE H. SHAW, 

Chemist, Dairy Division. 




WASHINGTON; 

GOVERNMENT PRINTING OFFICE. 

1917. 



Digitized by tine Internet Archive 
in 2010 witli funding from 
Tine Library of Congress 



littp://www.arGliive.org/details/Gliemicaltestingo01unit 



A._i2. Issued May 10, 1917. 

u. s. (department of agriculture, 

BimEAU OF ANIMAL INDUSTRY., 

A. D. MELVIN, Chief. 



CHEMICAL TESTING OF MILK 
AND CREAM. 



BY 



ROSCOE H. SHAW, 

Chemist, Dairy Division. 




WASHINGTON; 

GOVERNMENT PRINTING OFFICE. 

1917. 



'^ 



5.^t!. 






n 



D. of d; 

JUN ^2 1917 






1^^ 



CHEMICAL TESTING OF MILK AND 
CREAM.i 



CONTENTS. 

Page. 

Chemical nature of milk 3 

Testing f or fat ... : 5 

Testing milk for fat 1 5 

The Babcock test 7 

Testing cream for fat ] 8 

Testing skim milk for fat 23 

Testing buttermilk and whey for fat 25 

Preserving samples 25 

Cleaning the test bottles 25 

Determination of total solids in milk 26 

Determination of specific gravity of milk 30 

Calculating total solids by formula 32 

Determination of acidity of milk and cream 36 

Manns's acidity test 37 

Detection of preservatives 38 

Chemicals and apparatus used in the chemical 

analysis of milk and cream 40 

Comparison of metric and customary weights and 

measures 41 

Comparison of Fahrenheit and Centigrade ther- 
mometer scales 41 

CHEMICAL NATURE OF MILK. 

In order to follow intelligently the methods for testing 
milk and cream some knowledge of the chemistry of milk 
ia essential. From a chemical standpoint milk is a very 
complex substance. The component parts may, however, 

1 This is a reprint, \Yith slight revision, of a publication issued Feb- 
ruary 17, 1916, under the same title. In its preparation free use has been 
made of the various publications on the subject, particularly "Testing 
Milk and Its Products," by E. H. Farrington and F. W. Woll (Madison, 
Wis., 1911), and "Modern Methods of Testing Milk and Its Products," 
by L. L. Van Slyke (New York, 1907). 

(3) 



be classified into a few well-marked groups, as follows: (1) 
Water, (2) fat, (3) nitrogenous constituents, (4) sugar, and 
(5 ) ash . The components other than water are collectively 
known as total solids or milk solids, and the solids other 
than fat as solids not fat. Milk serum, or more properly 
milk plasma, is the term used to denote the milk minus 
the fat; hence the terms serum solids and plasma solids 
are synonymous with solids not fat. 

lYater. — ^The water in milk varies from 82 to 90 per cent. 
The usual variation in mixed-herd milk is much less and 
is probably covered by 84 to 88 per cent. 

Fat.— The fat in milk— milkfat or butterfat— ip not in 
solution but exists as an emulsion of microscopic glob- 
ules so small that a single drop of average milk contains 
more than one hundred millions of them. These glob- 
ules, even in milk from one cow, are not all of the same 
size. Some may be two or three times the size of others, 
the average size depending upon several factors, the 
principal one of which is the breed of the animal. Chem- 
ically the fat is not a single compound but a mixture of 
several compounds known as glycerids. Some of thes'e 
glycerids are common to all fats, while others are pecuUar 
to butter. This fact is made use of in detecting oleo- 



margarin. 



Cow's milk usually contains from 3 to 6 per cent of fat, 
depending very largely upon the breed of the animal. 

Nitrogenous constituents.— These are principally casein 
and' albumin, with traces of less important nitrogenous 
compounds. The coagulum, or curd, produced when 
rennet, dilute acids, or certain other chemicals, are added 
to milk, is chiefly casein. Albumin is the flaky precipi- 
tate produced by heating whey or skimmed milk from 
which the casein has been removed. In constitution and 
behavior it closely resembles white of egg. Casein is not 
really in solution in the milk, but exists in an extremely 
fine colloidal condition in combination with some of the 
ash constituents. With an appropriate filter of clay it is 
possible to separate it from the water. Albumin is in true 
solution in the water of the milk. Frequently, but im- 
properly, the term casein is applied to all the nitrogenous 
constituents in milk. Sometimes the term total proteins 



is used in referring to the nitrogenous constituents takeii 
as a whole. The amount of casein in average cow's milk 
varies from 2 to 4 per cent and the albumin from 0.5 to 
0.8 per cent. 

Sugar. — Milk sugar, or lactose, belongs to a group known 
as carbohydrates and is a white substance less sweet in 
taste than cane sugar. Milk sugar is broken up into lactic 
acid by the action of bacteria, this bringing about the sour- 
ing of milk. Milk sugar is in solution in the water of the 
milk and is present to the extent of from 3.5 to 6 per cent. 

Ash. — The ash, or the mineral part of milk, exists to the 
amount of about 0.75 per cent and consists largely of the 
chlorids and phosphates of sodium, potassium, magnesium, 
and calcium. 

AVERAGE CHEMICAL COMPOSITION. 

The table below gives the average of more than 5,000 
analyses of milk at the New York State Agricultiu-al Exper- 
iment Station, Geneva: 

Per cent. 

Water 87. 1 

Total solids 12. 9 

Fat 3.9 

Casein 2. 5 

Albumin 7 

Sugar 5.1 

Ash 7 

TESTING FOR FAT. 

In the following remarks on the testing of milk and 
cream the aim will be to present the subject in such man- 
ner that it may be followed by those who have had neither 
chemical training nor a course of any sort in milk testing. 
To those who have had such training the following pages 
will doubtless appear very elementary and overburdened 
with detail. 

TESTING MILK FOR FAT. 

Preparing the sample for testing. — As before mentioned, 
fat is not in solution in milk, but is in an emulsion of very 
fine globules. These, being lighter than the surrounding 
serum, tend to rise, carrying with them some of the other 
solids, resulting in the familiar creaming of milk. Before 



the test can be made a homogeneous mixture must be ob- 
tained. This can best be obtained by pouring the milk 
several times from one vessel into another. When the 
sample is small, beakers are convenient for this purpose, 
and if the sample has not remained in the container more 
than a few hours, pouring back and forth four or five times 
is sufficient. When, however, the sample haiB stood for 
some time in the container, the cream layer is liable to be 
hard and to adhere to the walls . This is particularly true of 
preserved samples. In such event it is well to place the 
container in warm water until the cream has become soft- 
ened and can then be easily removed. Care must be taken 
that none of the cream is left on the cover of the container; 
if, however, any is left, a brush such as ia used in cleaning 
beakers is useful in dislodging it. 

The sample must always be well mixed immediately 
before measming out a charge for testing. If several 
charges are to be measured out, the sample must be mixed 
each time. Thorough mixing is absolutely necessary for 
accurate work. 

Partially churned milh. — Mlk from some cows, notably 
of the Jersey breed, churns very easily and sometimes a too 
vigorous agitation in the mixing of such milk results in 
some of the fat collecting in small granules which refuse to 
emulsify again. This also frequently happens when the 
milk is sent a long distance in partially filled containers. 
These granules are easily recognized, and when they are 
present special treatment is required to prepare the sample 
for testing. A little ether equal in volume to 5 per cent 
of the milk may be added, and the container stoppered and 
vigorously shaken. The ether will dissolve the granules 
and the solution will mix with the milk. A fairly accurate 
charge may now be quickly removed, but the percentage 
obtained must be corrected for the volume occupied by the 
ether. 

Another and perhaps a better way to treat churned milk 
is to place the container in hot water until the milk has 
attained a temperature of about 110° F. In a few minutes 
at this temperature the granules will have melted. The 
container is then vigorously agitated and a charge for test 
immediately measured out. 



The partial churning of the samples is not a frequent 
occurrence and with proper care can always be avoided. 
When samples are to be sent a considerable distance, the 
containers should be completely filled so that no space is 
lej t at the top. A good way is to fill a bottle to overflowing 
with the mixed sample and then to insert a rubber or cork 
stopper haAang a hole about one-eighth of an inch in diame- 
ter. As the stopper goes to its place the milk will spurt 
out through the hole; the hole is then filled with a piece 
of glass rod or a wooden plug. When treated in such 
manner milk will not churn. 

Sour milk. — ^While the souring of milk does not affect 
the fat, it is impossible to obtain a representative charge 
from curdled milk without special treatment. In order to 
obtain a good mixture, it is necessary to dissolve the curd. 
This may be accomplished by adding 5 or 10 per cent by 
volume of a strong solution of either caustic soda or potash; 
strong ammonia water may also be used. The alkali must 
be thoroughly mixed with the milk imtil it is completely 
liquid. The charge for test must be immediately meas- 
ured out and a correction made in the final percentage for 
the volume occupied by the alkali solution. If desired, 
the powdered alkali may be added directly to the milk in 
small portions at a time, being sure that one portion is dis- 
solved before another is added, and agitating until the milk 
has become liquid. No correction is necessary for the 
volume occupied by the powdered lye. When making a 
fat test on milk containing alkali, special precautions 
must be observed in adding the sulphuric acid, as an ex- 
cessive amount of heat is generated and the contents of 
the test bottle may be thrown out. When alkali is used, 
slightly more acid is required. 

THE BABOOCK TEST. 

The Babcock test for fat in dairy products, named for its 
inventor, Dr. S. M. Babcock, chief chemist of the Wiscon- 
sin agricultural experiment station, is based upon the 
fact that strong sulphuric acid will dissolve the serum 
solids in milk and set the fat free from its emulsion. In 
conducting the test the charge is placed in a specially 
constructed test bottle and mixed with the proper quan- 

83460''-17 2 



8 



tity of sulphuric acid. The acid performs other functions 
than the simple solution of the serum solids. Much heat 
is developed by its action, and this causes the fat globules 
to lose their individuality and run together, a condition 
which greatly facilitates the separation from the serum, 
and this separation is still further accelerated by the 



^ 



_I0 
=-9 

E-8 

=-7 

5-5 
5-4 




m 



=2j 



=4J 



aj 



d 



dj 



Fig. 1.— Old type of 
Babcock milk-test 
bottle. 



C&-J 



^--^ 



Fig. 2.— Type of Babcoek 
milk-test bottle conforming 
to the requirements of the 
United States Bureau of 
Standards, and showing 
graduations. 



increase in specific gravity of the serum caused by the 
presence of the heavy sulphuric acid. When the solution 
of the serum solids is effected, the complete separation of 
the fat and serum is accomplished by whirling in a centri- 
fuge. The fat is gradually driven into the graduated neck 
of the bottle and the percentage read directly. 



/ 



Test bottles. — The Babcock-test bottle for milk, as shown 
in figure 1, consists of a body holding about 50 eubic centi- 
meters and the neck graduated so that the percentage of 
fat may be read directly. Seventeen and one-half cubic 
centimeters are used in the test, and this volume of 
average milk weighs almost exactly 18 grams. At the 
temperature at which the bottles are standardized the 
specific gravity of butterfat is about 
0.9. Two cubic centimeters weigh twice 
0.9, or 1.8 grams, which is just one- 
tenth of the weight of the charge used in 
the test bottle. The volume between 
and 10 per cent in the neck should, there- 
fore, be 2 cubic centimeters, if the bottle 
has been correctly standardized. Each 
unit per cent is represented by a volume 
of 0.2 cubic centimeters in the neck. The 
old types of bottles were 10 per cent bot- 
tles, the smallest subdivision being 0.2 per. 
cent. In the more recent typesi, notably 
those made to conform to the specifica- 
tions of the United States Bureau of Stand- 
ards, the necks are somewhat smaller in 
diameter and read only to 8 per cent, and 
the smallest subdivision is 0.1 per cent. 
(Fig. 2.) The 8 per cent bottle is consid- 
ered the more accurate of the two, and has 
come into more general use. 

Milk pipette. — The charge for the Bab- 
cock test for milk is measured rather than 
weighed, the measuring instrument being 
a pipette graduated to deliver 17.5 cubic 
centimeters of milk. These pipettes, filled to their 
graduation mark, hold 17.6 cubic centimeters. The 
extra 0.1 cubic centimeter is allowed for the milk 
which clings to the walls. Pipettes may be obtained 
which conform to the requirements of the United 
States Bureau of Standards. (Fig. 3.) 



U 

Fig. 3.— Pipette 
holding 17.6 
cubic centi- 
meters, used 
in measuring 
milk in the 
Babcocktest. 



10 



Acid measure. — This may be either a simple glass cylin- 
der graduated to deliver 17.5 cubic centimeters^ or one of 
the more complicated devices shown in figures 4, 5, and 6. 
A convenient little device is the small glass dipper (fig. 7) 
by which the proper quantity of acid may be dipped out 
of a larger container and poured into the test bottle. 

The centrifugal machine. — This is commonly called the 
Babcock tester, and various types are on the market, rang- 



17.5 
c.c 



17' 





Fig. 4.— Simple 
acid graduate. 



Fig. 5.— Burette 
for measuring 
the acid. 



Fig. 6.— a combined bottle 
pnd acid measure. 



ing from the small, two-bottle hand tester to the large 
steam turbine or electric tester, accommodating 24 or 
more bottles. (See figs. 8, 9, 10, and 11.) They all con- 
sist mainly of a horizontal revolving disk or wheel pro- 
vided with swinging sockets to hold the bottles. At rest 
these sockets allow the bottles to stand upright, but when 
in motion, the centrifugal force causes the sockets to 
swing outward, bringing the bottles to a horizontal posi- 
tiouj with the necks toward the center. Where steam 



11 



pressure is available, a steam turbine tester is strongly 
recommended for the reason that it maintains a uniform 
motion under a definite pressure and at the same time the 
steam keeps the bottles warm and supplies the hot water 
required. Whatever kind of tester is used, it must be 
firmly secured to a rigid support. There must be no 
shaking or trembling of the tester when in motion. 

^ac?.— The acid used in the Babcock test is the commer- 
cial sulphuric acid, sometimes called oil of vitriol, and 
should have a specific gravity of between 1.82 and 1.83. 
It should be kept in glass bottles or jugs, preferably with 
glass stoppers. Rubber stoppers will last for a time, but 
the use of cork stoppers is not permissible, as cork is rapidly 
attacked by the acid. Owing to the property of sulphuric 




Fig. 7.— a dipper made entirely of glass and holding 17.5 cubic centi- 
meters for measuring acid in the Babcock test. 

acid of absorbing water from the air and thus diluting 
itself, it can not be kept in open containers. 

Sulphuric acid is an extremely corrosive liquid, which 
attacks the skin, the clothing, wood, and most of the com- 
mon metals. Should the acid be spilled on the clothing, 
it should be immediately washed off with plenty of water, 
and ammonia water applied; this in turn must also be 
washed off. Unless the acid is washed off immediately 
after contact with the skin, severe burns will result. Acid 
spilled on the table or floor may be neutralized with wash- 
ing soda or other alkali. Lead is the only common metal 
not attacked by this acid. If much testing is to be done, 
it is a good plan to cover the testing table with sheet lead. 

Testing strength of acid.— As already mentioned, the 
specific gravity of the sulphuric acid used should be 
between 1.82 and 1.83. It is much better to purchase it 
guaranteed of the proper strength than to bother with 
diluting the stronger acid. Creamery supply houses han- 



12 




Fig. 8.— a 2-bottle hand tester. 



die acid guaranteed to be of the proper strength, and if 
kept in well-stoppered containers it will not change. For 
the benefit of those who prefer to test the acid themselves, 
the following directions are given: 

Use of the add hy- 
drometer. — This is a 
hydrometer designed 
only for liquids hav- 
ing a specific gravity 
about that of concen- 
trated sulphuric acid. 
(See fig. 12.) It is 
standardized at 60° F. , 
and for correct results 
must be used with acid 
at that temperature 
only. The acid at this 
temperature is poured into the hydrometer cylinder and 
the hydrometer allowed to float in it. When it has come 
to rest, the point on the scale intercepting the surface of 
the acid indicates the specific gravity. If it is much under 
1.82 it can not be used for 
testing milk, and should 
be discarded and a fresh 
lot of acid obtained. If it 
is above 1.83 it may be 
diluted with water until it 
is of the proper strength. 
There are two ways of 
doing this. The acid may 
be exposed to the air un- 
til it absorbs sufficient 
water to lower its specific 
gravity; this is the safest and best way if the specific 
gravity of the acid is not much above the standard. 
The second way is to mix the acid with a small quantity 
of water. A small quantity of water is placed in a bottle 
or jar and the acid poured into it. Never pour water into 
acid, as a serious accident may result. After the mixture 
has cooled to 60° F. it is again tested with the hydrometer 
and the process repeated if necessary. 




Fig. 9.— a hand tester for 12 bottles. 



13 



DIRECTIONS FOR MAKINO THE BABCOCK TEST WITH MILK. 

Measuring the charge. — Directions have already been 
given for preparing the sample for the test. The milk is 
poured from one container 
to another two or three 
times. The tip of the 
pipette is immediately in- 
serted and the milk sucked 
up with the mouth until 
it reaches a point well 
above the graduation mark 
on the stem; the dry fore- 
finger is then quickly 
placed over the mouth of 
the pipette. By slightly 
relaxing the pressure of 
the finger the milk is al- 
lowed to flow down until 
it just reaches the mark. 
The tip of the pipette is 




Fig. 10.— a type of steam tester 
with an arrangement for heating 
the water used in the test. 



now placed in the neck of the test bottle and the milk 

allowed to flow slowly down the side. The right way 

is to hold the pipette obliquely to the mouth of the 

test bottle as shown in 

figure 13. The wrong 

way is shown in figure 

14. If the bottle and 

pipette are held in the 

latter position the neck 

of the bottle may clog up 

and some of the milk 

run over the top. Care 

must be taken that none 

of the milk is lost during 

the operation. "When 
-A type of electric tester. ^^^^^^ ^j^ ^^^ ^^^ ^^^ 

run out of the pipette, the last drop is forced out with a 
puff of the breath. 

Adding the acid.— The temperature of the milk when the 
acid is added should be between 60° and 70° F., and the 
acid should be at about the same temperature. Seven- 




FlG. 11.- 



14 



teen and one-half cubic centiineters of the acid are meas- 
ured out, and, with the bottle held at an angle, carefully 
poured down the side, the bottle being turned slowly at 
the same time so that any milk adhering to the neck will 
be washed down . For two reasons the acid must not be 
poured into the middle of the test bottle; first, because it 






Fig. 12.— Hy- 
drometer and 
cylinder used 
in testing sul- 
phuric acid. 



Fig. 13.— The right way of add- 
ing milk to the test bottle. 
(Farrington and Well, Testing 
MUk and Its Products.) 



may form a plug in the neck, which may be driven out by 
the expansion of the air below ; and second, because the 
acid may partially mix with the milk and produce black 
particles which do not dissolve and later interfere with 
the reading of the test. The acid and milk should now 
be in two distinct layers without much of a dark layer 
between them. 



15 




Mixing the acid and the mill. — The acid is now mixed 
•with the milk by giving a combined rotary motion and 
gently shaking with the hand grasping the neck of the 
bottle, with the mouth of the bottle held away from the 
operator. When once commenced the mixing must not 
be interrupted until the solution is complete. The first 
effect of the acid on the milk 
is a curdling, wliich is sub- 
sequently dissolved. As the 
solution progresses the color 
changes first to a light yellow, 
then to dark yellow, then 
through various shades of vio- 
let to brown and finally to dark 
brown, if the acid is of the 
proper strength and the milk 
and acid are at the right tem- 
perature when united. Too 
strong or too warm acid pro- 
duces a dense black. If the 
milk has been presented with 
formaldehyde, a longer time is 
required to complete the solu- 
tion, owing to the toughening 
of the casein by that preserva- 
tive. Common errors of begin- 
ners are failure to mix the acid 
thoroughly with the milk and 
to continue the shaking imtil 
the solution is complete. A 
good plan is to shake the bottle 
for a minute or so after the so- 
lution is apparently complete. 
Although not necessary, it is 
preferable to centrifuge the bottles immediately, though 
they may be kept 24 hours if desired, in which case they 
must be placed in water from 170° to 180° F. for 15 to 20 
minutes before whii'ling. 

Centrifuging the bottles. — The bottles are now placed 
in the sockets of the centrifuge, taking care that they are 

83460—17 3 



^ 



/ 



Fig. 14.— The wrong way of 
adding the milk to the 
mUk bottle. (Farrington 
and Woll, Testing Milk 
and Its Products.) 



16 



equally distribiited about the wheel or disk so that the 
equilibrium of the latter is not disturbed. An even 
number of bottles should always be whirled. Should an 
odd number of tests be made a test bottle filled with water 
may be used to balance the machine. When the bottles 
are in place, the tester is covered in order to keep the bottles 
from getting cold and to protect the operator from flying 
glass and acid should any of the bottles break. The tester 
is now set in motion and the bottles whirled 4 to 5 minutes 
at proper speed. This will be sufiicient to bring prac- 
tically all the fat to the surface. In cold weather, if a 
hand tester is used, it may be necessary to pour hot water 
into the jacket of the tester to keep the bottles warm. 

Speed of centrifuge. — Farrington and Woll have calcu. 
lated the proper speed of testers with wheels of different 

diameters to be as follows: 

Revolutions 
of wheel 

Diameter of wheel in inches: per minute. 

10 1,074 

12 980 

14 - - 909 

16 848 

18 800 

20 , 759 

22 724 

24 693 

Adding the water. — ^With the pipette or with the device 
for the purpose attached to some steam testers, or in any 
other convenient manner, hot water is added to the bottles 
until the contents come nearly to the lower part of the 
neck. The cover is now replaced on the tester and the 
whirling repeated for two minutes. Hot water is again 
added until the fat reaches a point below the highest 
gi-aduation mark on the neck. It must never reach the 
top mark, or some of the fat may be lost. This time the 
water should be dropped directly into the fat in order to 
clear the fat of the light, fiocculent material which may be 
entangled in it and which would later interfere with the 
reading of the test. The whirling is repeated for another 
minute. The temperature at which the readings are taken 
is between 130° and 140° F., and this should be borne in 



o 



17 

mind -when the water is added, the object being to add 
the water at such a temperature that the temperature of 
the fat' at the close of the last whirling will be between 
these two figures. 

The water used should preferably be soft water or con- 
densed steam. The use of hard water is liable to cause 
trouble on account of its carbonates; these are decomposed 
by the acid, liberating carbon dioxid, which may cause 
foam on the top of the fat column and obscure the menis- 
cus. If soft water or condensed steam is not available, 
hard water may be used if, before heating it, a few drops 
of sulphuric acid are added. 

Reading the -percentage.— li the test has been successfully 
conducted, the fat will be in a clear, yellowish liquid 
column sharply separated from the clear and nearly color- 
less acid solution immediately below it and with no foam 
on top. The bottles should be kept warm either in the 
tester or in warm water until read, and the readings should 
always be made at between 130° and 140° F. The fat at 
this temperature will, if other conditions have been cor- 
rect, have a well-defined meniscus at both the top and the 
bottom. The readings are made from the extreme bottom 
of the lower meniscus to the extreme top of the upper men- 
iscus. Figure 15 shows this graphically. An ordinary 
pair of dividers is useful in making this reading. The 
points are placed at the upper and lower limits, then 
lowered until one point is at the mark ; the other point 
will indicate on the scale at the correct percentage for the 
sample tested. 

In some steam testers where the exhaust steam escapes 
into the jacket and no ventilation is provided, the tem- 
perature of the bottles will be too high. In such case, the 
bottles must be allowed to cool to 130° to -140° F. by plac- 
ing them in water at that temperature for several minutes 
before making the reading. 

Imperfect tests. — If the foregoing directions have been 
strictly followed, a perfect test should result. It is not to 
be expected, however, that the beginner will always meet 
with success. The next two paragraphs may be helpful in 
locating the trouble. 



18 



6.. 

c- 



-c/ 



a.. 



An imperfect test is caused by one of three things: 
(1) Foam on the fat column obscuring the upper menis- 
cus; (2) a dark-colored fat column containing dark parti- 
cles and with dark particles obscuring the lower meniscus; 
(3) a light-colored fat column containing white, curdy- 
material obscuring the lower meniscus. 

The first is caused by using hard water. Any one or a 
combination of the following may cause the second trou- 
ble: (a) The acid was too strong; {b) too 
much acid was used; (c) the acid was too 
warm when added to the milk; {d) the 
milk was too warm when the acid was 
added; (e) the acid was dropped directly 
into-the milk ; (/) the mixing of the acid 
and the milk was interrupted before the 
solution was complete; or (g') the acid and 
milk were allowed to stand too long in 
the test bottle before being mixed. The 
tliird trouble is caused by one or more of 
the following: (a) The acid was too weak; 
(b) too little acid was used; (c) the acid 
was too cold when added to the milk; 
{d) the milk was too cold when the acid 
was added; or (e) the mixing .was not 
continued long enough to dissolve all the 
serum solids. 

Tested Bahcock glassware. — Babcock-test 
bottles and pipettes should always be 
tested and found correct before being used. 
It is now possible to purchase test bottles 
and pipettes which have been tested and 
approved by the United States Bureau 
Many States also have officials empowered 
to test and approve Babcock glassware. The best way is 
to purchase it already tested by the Bureau of Standards, 
or to have it made to conform to the requirements of that 
bureau and then tested by a State official. 

TESTING CREAM FOR FAT. 

While in a general way cream is tested by the Babcock 
test in much the same manner as milk, there are some 



Fig. 15.— Show- 
ing metliod of 
reading fat 
c olumn in 
milk testing. 
Read from a 
to 6, not o to 
c, nor o to d. 

of Standards. 



19 



modifications that must be observ^ed. The range of fat in 
cream, and consequently the specific gravity, is much 
greater than in milk, so that 17.5 cubic centimeters do not 
necessarily represent 18 grams, as in the case of milk. 
Cream also varies in consistency, some being thin and some 
thick; therefore in some cases much more would adhere 
to the walls of the pipette than in others. For these rea- 
sons cream can not be accurately measured. The charge 
for the test must be weighed into the test bottle. 

Cream-test bottles. — The cream-test bottles used in the 
Babcock test are of various designs. (See figure 16.) 
Those conforming to the requirements of the United 
States Bureau of Standards differ from milk bottles only 
in the gi'aduations and in the length and diameter of the 
neck. Test bottles are made for both an 18-gram and a 
9-gram charge. 

Cream-test balances. — Several types of balances designed 
for weighing cream charges are on the market (figs. 17,18, 
and 19). The small torsion balances prove to be very sat- 
isfactory if care is taken that the important metal parts 
are not allowed to rust. Balances should be tested for 
sensitiveness from time to time and should always be kept 
in perfect condition. 

Preparing cream for testing. — The point never to be lost 
sight of in testing cream or milk is that the small quantity 
taken for the test must be truly representative. No matter 
how carefully the test is carried out, if the charge taken 
does not accurately represent the cream or milk to be 
tested, the results will be worthless. The prepai'ation of 
cream for testing does not differ materially from that of 
milk. The fat must be evenly distributed, and if there are 
no lumps this can be accomplished by poiuing from one 
receptacle to another, warming the cream slightly if cold. 
If lumps are present, it has been advised to pass the cream 
through a fine sieve, rubbing the lumps through with the 
fingers and then mixing as usual. If the cream has stood 
for some time in the sample jar, the top may have become 
hard, leathery, and difficult to remove. In this case, the 
jars should be set in warm water until the contents have 
reached 100° to 110° F., when the cream will be soft and 
can be easily removed. 



20 







Fig. 16.— Types of 9-gram and 18-gram cream bottles conforming to the 
reqitirements of the United States Bureau of Standards. 



21 



Weighing the charge. — After the sample has become homo- 
geneous throughout, the charge is quickly weighed into 
the test bottle. The weight of the charge depends upon the 




Fig. 17.— Type of knife-edge cream balance. 

style of bottle used. For this purpose the 9-gram bottle 
is recommended. A pipette is useful in conveying the 
cream to the test bottle, as the flow can be easily controlled 




Fig. 18.— Type of torsion balance for single bottle. 

and checked on the drop when the pointer of the balance 
indicates that the correct quantity has been run in. This 
weight must be exact, and some experience is necessary 
before the charges can be quickly and accurately weighed. 



22 



Completing the test. — -Instead of adding a measured 
quantity of sulphuric acid to the cream in the test bottle, 
as is done with milk, the best way is to add the acid until 
the mixture assumes the color of coffee to which cream has 
been added. ^ The quantity of acid required to produce 
this color varies with the percentage of fat in the cream. 
If the cream and acid when mixed are about 70° F., about 
one-quarter or one-half the regular quantity (4 to 8 cubic 
centimeters) of acid (specific gravity 1.82 to 1.83), depend- 
ing upon the percentage of fat, will be required for a 9- 
gram charge. After adding the acid to the cream, the 




Fig. 19.— Type of balance for several bottles. 

procedure up to the reading of the percentage is exactly 
the same as in the milk test. After the final whirling, the 
test bottles are submerged to a point above the fat column 
in water at 135° to 140° F. in a suitable tank. After re- 
maining in this tank for about 15 minutes they are re- 
moved and the readings quickly made. The important 
difference between reading the cream test and the milk 
test is that in the cream test the fat column included is 
from the bottom of the lower meniscus to the bottom, not 
the top, of the upper meniscus. (See fig. 20.) 

1 O. F. Hunziker and H. C. Mills, Testing Creamfor Butter Fat, Indi- 
ana Agricultural Experiment Station, Bui. 145. June, 1910. 



23 



K^ 



Some operators prefer to destroy the upper meniscus by 
dropping into the bottle at this point a few drops of a 
liquid in which the fat is not soluble. Glymol (petrolatum 
liquidum, U. S. P.), known commercially as white min- 
eral oil, gives satisfactory results and may be purchased 
at almost any drug store. If desired it 
may be colored with alkanet root.^ If 
glymol is used, the fat column included 
in the reading is from the bottom of the 
lower meniscus to the line between the 
fat and the glymol. If the fat column is 
read with the upper meniscus intact, care 
must be taken that the eye is on a level 
with the points on the scale at which the 
readings are made; otherwise an error 
will be introduced. 



16 
/5 
/<? 
/J 
/-? 

/O 



TESTING SKIM MILK FOR FAT. 



zC^ 



-■■a 



,While in general skim milk is tested 
with the Babcock test in the same manner 
as whole milk, the test does not apply to 
it with the same degree of accuracy. The 
reason for this is perhaps as follows : The 
fat in milk, as already shown, exists as 
fat globules of different sizes. In the 
process of skimming either by the cen- 
trifugal separator or by gravity the force 
tending to separate the fat from the other 
milk constituents acts more strongly upon 
the larger globules; consequently there is 
a much larger proportion of small globules 
in skim milk than in the whole milk. 
In the Babcock test the fat is driven into 
the neck of the test bottle by centrifugal force. Here 
again the force acts more strongly upon the larger glob- 
ules. Some of the smaller globules never reach the neck 
of the test bottle. This is compensated for in testing 
whole milk by the liberal reading of the fat column — that is, 



Fig. 20.— Show- 
ing method 
of reading fat 
column in 
cream testing. 
Read from a 
to c, not a to 6, 
nor a to d. 



1 Hunziker and Mills, loc. cit. 



24 



by reading from the bottom of the lower meniscus to the 
top of the upper one. In skim milk, however, since most 
of the globules are small, a greater proportion of them fail 
to be driven into the neck of the test bottle ; consequently 
the reading is too low and does not give the true percent- 
age of fat. The skim-milk test is valuable for testing the 
completeness of the skimming, but its re- 
sults must not be interpreted too strictly. 

The skim-milk test bottle differs from 
the whole-milk test bottle in having two 
necks, one of small bore graduated to read 
hundredths per cent for the fat column, 
and one extending nearly to the bottom of 
the bottle for filling. (See fig. 21.) 

Seventeen and one-half cubic centime- 
ters of the skim milk is placed in the test 
bottle by means of the filling tube. Twen- 
ty cubic centimeters of sulphuric acid is 
added in two portions of 10 cubic centime- 
ters each, shaking after each addition. 
Great care must be taken while shaking 
to be sure that no particles reach the fat 
tube; otherwise it will become plugged 
and the test ruined. The test bottles are 
placed in the tester with the filling tubes 
toward the center. The first whirling is 
continued one or two minutes longer than 
when testing whole milk. As in whole-milk 
testing, hot water is added in two portions, 
the second one bringing the fat about half way up the tube. 
The reading should be made immediately after the final 
whirling. If the fat is in the lower part of the tube it may 
be forced into the graduated part by the pressure of the 
finger at the mouth of the filling tube. Some skim-milk 
test bottles have the mouth of the fat tube enlarged to 
receive a rubber stopper which may be used to adjust the 
fat column for reading. 



Fig. 21. 



25 

TESTING BUTTERMILK AND WHEY FOR FAT. 

Buttermilk and whey are tested in exactly the same 
manner as skim milk, except that whey, havjng less solids 
not fat, requires but about half the quantity of acid. 

PRESERVING SAMPLES. 

If for any reason it is desired to keep a sample of milk 
or cream for a few days before testing it, a preservative 
should be added to prevent decomposition. Formalin 
(which is a 40 per cent solution of formaldehyde) , corrosive 
sublimate (mercuric chlorid), or potassium bicluomate 
are used for this pm-pose. Formalin has the advantage of 
being a liqmd and easily handled; on the other hand, it 
has the property of toughening the casein and rendering it 
more difficult to dissolvelater in the sulphuric acid. One 
cubic centimeter should keep a pint or quart of milk or 
cream for two weeks or more. Corrosive sublimate, while 
the most powerful of the three, is a deadly poison. Sam- 
ples preserved with it should be colored in some way to 
indicate the presence of the poison. Tablets of corrosive 
sublimate containing coloring matter are on the market. 
If potassium bichi'omate is used, the samples should be 
kept in a dark place; 15 to 20 grains is sufficient to pre- 
serve a pint for a reasonable length of time. 

CLEANING THE TEST BOTTLES. 

After the test, and before the test bottles have become 
cold, they should be emptied with a shake or two to loosen 
the grayish-white deposit of calcium sulphate which accu- 
mulates on the bottom. A convenient device is shown 
in figure 22. Tliis consists of a 5-gallon stone jar with a 
wooden cover in which one-half-inch holes have been 
bored. After the test the necks of the bottles are placed in 
the holes and the contents allowed to run out, giving each 
bottle an occasional shake. The bottles, after their con- 
tents have escaped, should be rinsed twice with very hot 
water and then in a warm dilute solution of lye, soap 



26 



powder, or other cleansing powder. They should then 
receive a final rinsing and be placed in a suitable rack to 
drain. 




DETERMINATION OF TOTAL SOLIDS IN MILK. 

As brought out earlier in this circular, milk is composed 
of water and the various solids collectively known as total 
solids or milk solids. Manifestly the simplest way of 
determining the amount of total solids in a given quantity 
of milk is to separate them from the 
water and weigh them. This is pre- 
cisely the manner in which the total 
solids in milk are determined in the 
laboratory. A small quantity of milk 
is weighed into a shallow flat-bottomed 
dish and then heated until all the water 
is driven off. During this evaporation 
the milk must not be heated more than 
a degree or so above the boiling point 
of water, because at a higher tem- 
perature some of the solids are decom- 
posed. 

Ovens. — Several types of ovens are used for holding the 
milk at the right temperature during the evaporation. 
The simplest type is perhaps the so called double-walled 
drying oven (fig. 23) . This piece of apparatus is really one 
oven inside of another, the space between the two being 
partly filled with water. A burner placed under the oven 
boils the water, and the remaining space between the 
walls is filled with steam, maintaining a constant tempera- 
ture in the inner compartment which holds the milk 
dishes. Unless carefully watched, the oven will "boil 
dry," to prevent which it is a good plan to attach some 
sort of condenser. The type of condenser known as the 
globe condenser is very satisfactory for this purpose. Some 
ovens are constructed with a constant-level attachment. 

Balance. — Nice weighings are required in the determi- 
nation of total solids in milk, and it is necessary to use the 



Fig. 22. — Tar 
with p e r - 
forated cover 
for use in 
emptying test 
bottles. 



27 



type of balance kno^vll as the analytical balance (fig. 24), 
the cream-test balance not being sensitive enough for this 
purpose. On the other hand, the analytical balance can 
not be used with advantage in weighing cream charges for 
the Babcock test. An analytical balance sensitive enough 
for the purpose can be purchased for from $30 to S40. A 
set of accurate analytical weights will also be required. 
Space does not permit directions for using the analytical 




Fig. 23.— Dou])le-walled drying oven. 

balance. If the operator is not familiar with its use, he is 
advised to consult some elementary treatise on quantita- 
tive chemical analysis. It must be borne in mind that 
the analytical balance is a very delicate instrument and 
should be treated accordingly. 

Desiccators. — A warm dish can not be accurately weighed 
on the balance because the heat creates air currents which 
buoy up the scale pan sufficiently to make the dish appear 



28 



lighter than really is the case. Again, many substances 
can not be exposed to the air without absorbing atmos- 
pheric moisture and in this way introducing an error into 
the weighing. For these reasons it is customary always to 
cool the dishes in a device known as a desiccator (fig. 25) 
before weighing them. A desiccator is a specially con- 
structed covered jar containing a substance like calcium 
chlorid, which attracts to itself all the atmospheric mois- 
ture in the inclosed space surrounding it. The desiccator, 
containing no moisture, will, of course, permit a substance 




FiG.,24.— Analytical balance. 

to be kept in it without absorbing any. The calcium 
chlorid, which forms a layer about 1 inch deep on the bot- 
tom of the desiccator, should be renewed as soon as it shows 
any signs of moisture. The cover of the desiccator should 
be removed only as often as is necessary, and then for the 
shortest possible time. 

Milk dishes. — These are commonly made of aluminum 
and should be from 2 to 2\ inches wide and about one-half 
inch deep (fig. 26). Each dish should bear a number by 
which it can be identified; this number may be scratched 
or pimched on the side. 



29 




Fig. 25. — Desiccator. 



charge, 



and should be 



Preparing the dishes. — After the dishes are clean and dry 
they should be placed in the drying oven for half an hour, 
then removed and placed in the desiccator until cool. 
They should be handled with for- 
ceps or crucible tongs, and as soon 
as they are cool they are weighed 
on the analytical balance. 

Weighing the charge. — After the 
milk has been thoroughly mixed, 
it is drawn up in a pipette and 
allowed to flow into the dish until 
a thin film just covers the bottom; 
the dish and milk are then quickly 
weighed. The weight of the 
empty dish subtracted from the 
last weight is the weight of the 
about 2 grams. 

Evaporating the water. — The dishes containing the milk 
are now placed in the oven, dried for about four hours, and 
then placed in the desiccator until cool, when they are 
weighed . They are then returned to the oven for 30 min- 
utes, after which they are cooled and weighed as before. 

If there is no loss in weight, 
or if there is a slight gain in 
weight during the 30 min- 
utes, it indicates that all the 
water is driven off, and this 
last weight minus the weight 
of the empty dish is the 
weight of the total solids in 
the charge taken. This multiplied by 100 and divided by 
the weight of the charge gives the percentage. If there 
are was a loss in weight dming the 30 minutes, the dishes 
returned to the oven and dried for another period or until 
they cease to lose weight. 

Determination of solids not fat. — The percentage of solids 
not fat, or serum solids, is found by subtracting the per- 
centage of fat from the percentage of total solids. 




Fig. 26.— Milk dish. 



30 



DETERME^ATION OF SPECIFIC GRAVITY OF MILK. 

For exact work the specific gravity of milk is deter- 
mined by comparing the weight of a volume of milk with 
that of an equal volume of pure water under controlled- 
temperature conditions. For inspection work an instru- 



r\ 




/ 



U7 



/ 



\ 




\ 




Fig. 27.— Westphal balance. 



Fig. 28. — Types of ordinary 
lactometers. 



ment known as the Westphal balance or the special 
lactometer described in Bulletin 134 of the Bureau of Ani- 
mal Industry, United States Department of Agriculture, 
is sufficiently acciu-ate. 

Westphal balance. — This instrument (fig. 27) consists of a 
pivoted beam graduated on one arm and bearing a plum- 



31 



met or float. The weights in terms of spe- 
cific gravity represent unity, tenths, hun- 
dredths, thousandths, and ten thousandths. 
With no weight on the beam it balances 
when the plummet floats in air. When 
the unit weight is in position, it balances 
when the plummet floats in pure water at 
the proper temperature. WTien the plum- 
met is submerged in a liquid heavier than 
water, such as milk, additional weights are 
required to bring the instrument to equi- 
librium. The speciflc gravity is read off 
directly from the value of the weights and 
their position on the beam. Detailed direc- 
tions usually accompany the instrument. 

Lactometers. — Most lactometers are not 
sensitive enough for determining the speci- 
fic gravity of milk if more than approximate 
figmes are required. The use of either the 
Westphal balance or the special lactom_ 
eter, previously mentioned, is advised. 
If, however, only approximate results are 
required the ordinary lactometer, of which 
there are several types on the market, will 
suffice. 

The lactometer (fig. 29) is used exactly in 
the same manner as is the hydrometer in 
testing sulphuric acid, directions for which 
are given on page 12. Care must be taken 
that the milk is at the temperature at which 
the lactometer is standardized and that the 
lactometer floats freely in the cylinder. 
The specific gravity of milk can not be 
taken until the milk is three or four hours 
old. The point on the scale of the lactome- 
ter where the surface of the milk intercepts 
represents the specific gravity which is 






a 

a 
1 

p 





CO 

d 
K 



32 



usually expressed in Quevenne aegrees.^ A slight 
meniscus will obscure the surface line, and it is necessary 
to estimate its depth. This will cause no error if it is 
remembered that the point to be read is at the surface of 
the milk and not at the top of the meniscus. 

A type of lactometer known as the New York board of 
health lactometer is in somewhat general use. The scale 
of this instrument does not give the specific gravity di- 
rectly, but is so arranged that milk having a specific gravity 
of 1.029 (at 60° F.) will read 100°. As the zero mark is the 
point to which it will sink when immersed in pure water, 
100° on the scale corresponds to 29° on the Quevenne scale. 
New York board of health lactometer degree may be con- 
verted into Quevenne degrees by multiplying by 0.29. 

CALCULATING TOTAL SOLIDS BY FORMULA. 

When the percentage of fat and the specific gravity of the. 
milk are known and only the closely approximate percent- 
age of total solids is wanted, it should be calculated by the 
Babcock formula. The following table and directions for- 
using it are taken from Bureau of Animal Industry Bulletin 
134: ' 

1 Quevenne degrees are converted into specific gravity by dividing by 
1,000 and then adding 1 to the quotient. This is done at a glance. For 
example, if the Quevenne reading is 32.5, the specific gravity is 1.0325. 



33 



Table I. — For determining total solids in milk frovi any 
given specific gravity and percentage of fat. 

[Per cent total solids.] 



Per- 


Lactometer reading at C0° F. (Quevenne degrees). 


cent- 
ageof 


























fat. 


26 


27 


28 


29 


30 


31 


32 


33 


34 


35 


36 


2.00 


8.90 


9.15 


9.40 


9.65 


9.90 


10.15 


10.40 


10.66 


10.91 


11.16 


11.41 


2.05 


8.96 


9.21 


9.46 


9.71 


9.96 


10.21 


10.46 


10.72 


10.97 


11.22 


11.47 


2.10 


9.02 


9.27 


9.52 


9.77 


10.02 


10.27 


10.52 


10.78 


11.03 


11.28 


11.53 


2.15 


9.08 


9.33 


9.58 


9.83 


10.08 


10.33 


10.58 


10.84 


11.09 


11.34 


11.59 


2.20 


9.14 


9.39 


9.64 


9.89 


10.14 


10.39 


10.64 


10.90 


11.15 


11.40 


11.65 


2.25 


9.20 


9.45 


9.70 


9.95 


10.20 


10.45 


10.70 


10.96 


11.21 


11.46 


11.71 


2.30 


9.26 


9.51 


9.76 


10.01 


10.26 


10.51 


10.76 


11.02 


11.27 


11.52 


11.77 


2.35 


9.32 


9.57 


9.82 


10.07 


10.32 


10.57 


10.82 


11.08 


11.33 


11.58 


11.83 


2.40 


9.38 


9.63 


9.88 


10.13 


10.38 


10.63 


10.88 


11.14 


11.39 


11.64 


11.89 


2.45 


9.44 


9.69 


9.94 


10.19 


10.44 


10.69 


10.94 


11.20 


11.45 


11.70 


11.95 


2.50 


9.50 


9.75 


10.00 


10.25 


10.60 


10.75 


11.00 


11.26 


11.51 


11.76 


12.01 


2.55 


9.56 


9.81 


10.06 


10.31 


10.56 


10.81 


11.06 


11.32 


11.57 


11.82 


12.07 


2.60 


9.62 


9.87 


10.12 


10.37 


10.62 


10.87 


11.12 


11.38 


11.63 


11.88 


12.13 


2.65 


9.68 


9.93 


10.18 


10.43 


10.68 


10.93 


11.18 


11.44 


11.69 


11.94 


12.19 


2.70 


9.74 


9.99 


10.24 


10.49 


10.74 


10.99 


11.24 


11.50 


11.75 


12.00 


12.25 


2.75 


9.80 


10.05 


10.30 


10.55 


10.80 


11.05 


11.31 


11.56 


11.81 


12.06 


12. 31 


2.80 


9,88 


10.11 


10.36 


10.61 


10.86 


11.11 


11.37 


11.62 


11.87 


12.12 


12.37 


2.85 


9.92 


10.17 


10.42 


10.67 


10.92 


11.17 


11.43 


11.68 


11.93 


12.18 


12.43 


2.90 


9.98 


10.23 


10. 48 


10.73 


10.98 


11.23 


11.49 


11.74 


11.99 


12.24 


12.49 


2.95 


10.04 


10.^9 


10.54 


10.79 


11.04 


11.30 


11,55 


11.80 


12.05 


12.30 


12.55 


3.00 


10.10 


10.35 


10.60 


10.85 


11.10 


11.36 


11.61 


11.86 


12.11 


12.36 


12.61 


3.05 


10.16 


10.41 


10.66 


10.91 


11.17 


11.42 


11.67 


11.92 


12.17 


12.42 


12.68 


3.10 


10.22 


10.47 


10.72 


10.97 


11.23 


11.48 


11.73 


11.98 


12.23 


12.48 


12.74 


3.15 


10.28 


10.53 


10.78 


11.03 


11.29 


11.54 


11.79 


12.04 


12.29 


12.55 


12.80 


3.20 


10.34 


10.59 


10.84 


11.09 


11.35 


11.60 


11.85 


12.10 


12.35 


12.61 


12.86 


3.25 


10.40 


10.65 


10.90 


11.16 


11.41 


11.66 


11.91 


12.16 


12.42 


12.67 


12.92 


3.30 


10.46 


10.71 


10.96 


11.22 


11.47 


11.72 


11.97 


12.22 


12.48 


12.73 


12.98 


3.35 


10.52 


10.77 


11.03 


11.28 


11.53 


11.78 


12.03 


12.28 


12.54 


12.79 


13.04 


3.40 


10.58 


10.83 


11.09 


11.34 


11.59 


11.84 


12.09 


12.34 


12.60 


12.85 


13.10 


3.45 


10.64 


10.89 


11.15 


11.40 


11.65 


11. 90 


12.15 


12.40 


12.66 


12.91 


13.16 


3.50 


10.70 


10.95 


11.21 


11.46 


11.71 


11.96 


12.21 


12.46 


12.72 


12.97 


13.22 


3.55 


10.76 


11.02 


11.27 


11.52 


11.77 


12.02 


12.27 


12.52 


12.78 


13.03 


13.28 


3.60 


10.82 


11.08 


11.33 


11.58 


11.83 


12.08 


12.33 


12.58 


12.84 


13.09 


13.34 


3.65 


10.88 


11.14 


11.39 


11.64 


11.89 


12.14 


12.39 


12.64 


12. 90 


13.15 


13.40 


3.70 


10.94 


11.20 


11.45 


11.70 


11.96 


12.20 


12.45 


12.70 


12.96 


13.21 


13.46 


3.75 


11.00 


11.26 


11.51 


11.76 


12.01 


12.26 


12.51 


12.76 


13.02 


13.27 


13.52 


3.80 


11.06 


11.32 


11.57 


11.82 


12.07 


12.32 


12.57 


12.82 


13.08 


13.33 


13.58 


3.85 


11.12 


11.38 


11.63 


11.88 


12.13 


12.38 


12.63 


12.88 


13.14 


13.39 


13.64 


3.90 


11.18 


11.44 


11.69 


11.94 


12.19 


12.44 


12.69 


12.94 


13.20 


13.45 


13.70 


3.95 


11.24 


11.50 


11.75 


12.00 


12.25 


12.50 


12.75 


13.00 


13.26 


13.51 


13.77 


4.00 


11.30 


11.56 


11.81 


12.06 


12.31 


12. 56 


12.81 


13.06 


13.32 


13.57 


13.83 


4.05 


11. .36 


11.62 


11.87 


12.12 


12.37 


12.62 


12.87 


13.12 


13.38 


13.63 


13.89 


4.10 


11.42 


11.68 


11.93 


12.18 


12.43 


12.68 


12.93 


13.18 


13.44 


13.69 


13.95 


4.15 


11.48 


11.74 


11.99 


12.24 


12.49 


12.74 


12.99 


13.25 


13.50 


13. 76 


14.01 


4.20 


11.54 


11.80 


12.05 


12.30 


12.55 


12.80 


13.05 


13.31 


13.56 


13.82 


14.07 


4.25 


11.60 


11.86 


12.11 


12.36 


12.61 


12.86 


13.12 


13.37 


13.62 


13.88 


14.13 


4.30 


11.66 


11.92 


12.17 


12.42 


12.67 


12.92 


13.18 


13.43 


13.68 


13.94 


14.19 


4.35 


11.72 


11.98 


12.23 


12.48 


12. 73 


12.98 


13.24 


13.49 


13.74 


14.00 


14.25 


4.40 


11.78 


12.04 


12.29 


12.54 


12.79 


13.04 


13.30 


13.55 


13.80 


14.06 


14.31 


4. 45 11. 84 


12.10 


12.35 


12.60 


12.85 


13.10 


13.36 


13.61 


13.86 


14.12 


14.37 



34 



Table I. — For determining total solids in milh from any 

given specific gravity and percentage o//a<— Contd. 

[Per cent total solids.] 



Per- 

cent- 

ageof 

fat. 



Lactometer reading at 60° F. (Quevenne degrees). 



26 



4.50;il. 
4.55!ll. 
4. 60 12. 



4.65 

4.70 

4.75 

4.80 

4.85:12. 

4.9012. 

4.9512. 



0012. 

05:12. 

1012. 
15 1 12. 
2012. 



5, 

5, 

5. 

5. 

5. 

5.25 

5.30 

5.35 

5.40 

5.45 



27 i 28 



1612. 
2212. 
2812. 
34 12. 
4012. 
4612. 
5212. 
5812. 
6412. 
70 12. 



29 30 31 32 



7613. 
8213. 
8813. 
94 13. 



33 34 35 



6713. 
7313. 
7914. 



36 



14.43 
14.49 
14.55 
14.61 
14.67 
14.73 



54 14.79 
60 14.85 
6614.91 
7214.97 



7815.03 
84 15.09 
90 15. 15 
96 15. 21 
02 15. 27 
0815.33 
14 15. 39 
20 15. 45 
2615.51 
32 15. 57 



5.50 

5.55 

5.60 

6.65 

5.70 

5.75 

5.80 

5. 85113. 

5.9013. 

5.95 13, 



14. 

14. 

14. 

14. 

14. 

14. 

14. 

15. 
86,15. 
9215. 



38 15. 63 
4415.69 
50 15. 75 



15.81 
15.87 
15.93 
15.99 
16.06 
86 16. 12 
92 16. 18 



6.00 
6.05 
6.10 
6.15 
6.20 
6.25 
6.30 
6.35 
6.40 
6.45 



8914. 



1914. 
2514. 



4014. 
4614. 



7615. 



9815. 
04 1 15. 
lOilS. 
16il5. 
2215. 
2815. 
34:15. 
4015. 
4615. 
5215. 



16.24 
16.30 
16.35 
16.42 
16.48 
16.54 
16.60 
16.66 
16.72 
16.78 



6.50 
6.55 
6.60 
6.65 
6.70 
6.75 
6.80 
6.85 
6.90 
6.95 



3114 
3714, 
4314, 
4914, 
5514, 



5614. 
6214. 
68 14. 
74il5. 
8015. 
8615. 
9215. 
9815. 



8215. 
8815. 
9415. 
00,15. 
0615. 
1215. 
18! 15. 
24 15. 



0815. 

1415. 
2015. 



5815. 
6415. 
7015. 
76 16. 
8216. 
8816. 
94 16. 
0016. 
0616. 
1216. 



8316. 
16. 



0816. 
1416. 
2016. 
26!l6. 
32; 16. 
3816. 
4416. 
5016. 



5716. 
6316. 
6916. 
7517. 



16.84 
16.90 
16.96 
17.02 
17.08 
17.14 
17.20 
17.26 
17.32 
17.38 



35 



Table II. — For determining total solids in milk from any 
given specific gravity and percentage of fat. 

PROPORTIONAL PARTS. 





Fraction 




Fraction 




Fraction 


Lactom- 


to be 


Lactom- 


to be 


Lactom- 


to be 


eter 


added to 


eter 


added to 


eter 


added to 


fraction. 


total 


fraction. 


total 


fraction. 


total 




solids. 




solids. 




solids. 


0.1 


0.03 


0.4 


0.10 


0.7 


0.18 


.2 


.05 


.5 


.13 


.8 


.20 


.3 


.08 


.6 


.15 


.9 


.23 



Directions for using the table. — If the specific gravity as 
expressed in Quevenne degrees is a whole number, the 
percentage of total solids is found at the intersection of 
the vertical column headed by this number with the hori- 
zontal column corresponding to the percentage of fat. 

If the specific gravity as expressed in Quevenne degrees 
is a whole number and a decimal, the percentage of total 
solids corresponding to the whole number is first found, 
and to this is added the fraction found opposite the tenth 
under "Proportional Parts." Two examples may sufiice 
for illustration: (1) Fat, 3.8 per cent; specific gravity, 32. 
Under column headed 32, 12.57 per cent is found corre- 
sponding to 3.8 per cent fat. (2) Fat, 3.8 per cent; spe- 
cific gravity, 32.5. The percentage of total solids corre- 
sponding to this percentage of fat and a specific gravity of 
32 is 12.57. Under "Proportional Parts " the fraction 0.13 
appears opposite 0.5. This added to 12.57 makes 12.70, 
which is the desired percentage. 

An inspection of the table shows that the percentage of 
total solids increases practically at the rate of 0.25 for each 
lactometer degree and 1.2 for each per cent of fat. This 
gives rise to Babcock's simple formula: Total solids= 
i L-l-1.2 F. (L=lactometer reading in Quevenne degrees 
and f=percentage of fat.) 

To illustrate the use of the formula the following ex- 
ample is given: Fat, 4 per cent; specific gravity, 32. In 
this case one-quarter of 32 is 8; 1.2 multiplied by 4 is 4.8; 
8 plus 4.8 equals 12.8, which represents the percentage of 
total solids. 



36 

This simple formula can be used in cases not provided 
for in the table. 

DETERMINATION OF ACIDITY OF MILK AND 

CREAM. 

Acidity in milk is attributable to two causes, (1) the pres- 
ence in milk of acid phosphates and perhaps of carbon 
dioxid, and (2) lactic and other acids produced by the 
decomposition of the milk sugar by bacterial action. 
When freshly drawn milk is acid to phenolphthalein, this 
acidity is from 0.07 per cent to 0.08 per cent and is owing 
to causes given under (1). Lactic acid is not present in 
freshly drawn milk; it develops only on standing. Milk 
is not soin: to the taste until it has a total acidity of at 
least 0.3 per cent. 

For convenience the total acidity of milk is usually 
calculated as lactic acid. The principle upon which the 
determination of acidity is based is the well-known 
chemical action of acids upon alkalies. To illustrate, the 
action of hydrochloric (sometimes called miniatic) acid 
on a solution of caustic soda may be taken. This acid 
has a sharp and very soxn- taste, while caustic-soda solu- 
tions have a soapy feel and a peculiar odor, and if suffi- 
ciently strong will attack the skin. If the solution of 
caustic soda is slowly added to the hydrochloric acid, the 
sour taste will gradually disappear until the exact point of 
neutrality is reached, when a new substance is produced — 
sodium chlorid, or common salt, which has neither the 
acid properties of the one not the alkaline properties of 
the other. The sense of taste, however, is not sufficiently 
sensitive to determine when the exact point of neutrality 
has been reached. Phenolphthalein is an organic com- 
pound, having the property, when in solution, of turning 
pink with alkalies and remaining colorless with acids. 
Such a substance is called an indicator because it indicates 
by a color change when a certain chemical reaction has 
taken place. 

There are several so-called acid tests before the public. 
The one known as Manns's acidity test is widely used and 
is conducted as follows: 



37 



MANNS'S ACIDITY TEST. 

Apparatus required: 
One 50 cubic centimeter glass burette graduated to 

tenths, with stopcock. 
One 50 cubic centimeter pipette. 

One 250 cubic centimeter beaker, or a white teacup. 
One support for burette. 
Glass stirring rods. 

One-tenth normal solution of caustic soda, each cubic 
centimeter of which will neutralize 0.009 gram of 
lactic acid. 
An alcoholic solution of phenolphthalein made by 
dissolving 10 grams in 300 cubic centimeters of 90 
per cent alcohol. 
One who has not had training in chemistry should not 
attempt to make the tenth-normal solution of caustic soda, 
as it can be purchased to better advantage from any chem- 
ical supply house. 

Conducting the test. — -With the pipette 50 cubic centi- 
meters of the milk or cream is measured into the beaker or 
cup and 2 or 3 drops of phenolphthalein solution added. 
If the cream is thick, it may be slightly warmed. The 
burette is filled with the tenth-normal caustic-soda solu- 
tion so that the lowest part of the meniscus is level with 
the zero point on the graduations. The solution is now 
run slowly from the burette into the milk or cream, stir- 
ring with a glass rod at the same time. It will be noticed 
that the alkali at once produces a pink color where it 
strikes; this, however, disappears on stirring. As more 
and more of the alkali is added, it will be noticed that the 
pink color is slower in disappearing until finally it becomes 
permanent for a time. Toward the end, the alkali should 
be added drop by drop and the very first appearance of a 
permanent faint pink is the signal that the neutral point 
has been reached. This color, on account of absorption 
of carbon dioxid from the air, will disappear after standing 
a short time. The number of cubic centimeters of alkali 
used can be learned by referring to the burette, remember- 
ing that the reading is taken from the lowest point of the 
meniscus. 



38 

The percentage of acidity is calculated by multiplying 
the number of cubic centimeters of alkali solution u.-<od 
by 0.009 and di\iding by the number of cubic centimeters 
of milk or cream taken, the quotient being multiplied by 
100. Thus: 

u . f -r* c. c. alkaliX^OOl) 

Percentage of acidity^ ^^^^^,^ ^^^^^^ XIOO. 

If 50 cubic centimeters of the sample required 10 cubic 
centimeters of the alkali to neutralize, the percentage of 
acidity would be 

-^%r^X100, or 0.18 per cent. 

DETECTION OF PRESERVATIVES. 

The preservatives usually met with are formaldehyde, 
borax, and boric acid, and these are not difficult to detect 
if care is used in conducting the tests. Until one is thor- 
oughly familiar with the tests it is a good plan to run three 
samples together, one being the suspected sample, one 
which is known to contain the preservative looked for, and 
one known to be free from that jireservative. 

Formaldehyde. — There are two well-known tests for 
detecting formaldehyde, one known as the Ilehner test 
and the other as the Leach test. 

In the Hehner test, about 5 cubic centimeters of the 
milk is placed in a G by J inch tc.-^t tube, and then about 
the same quantity of concentrated sulphuric acid to which 
a trace of ferric chlorid has been added. The acid is 
allowed to run dnwn the .'^ide of (he test tube so as not to 
mix with the milk. In a few minutes the presence of 
formaldehyde will be indicated by a violet coloration at 
the juncture of the milk and the acid. This must not be 
confused with the charring of the milk by the acid. A 
modification which avoids this charring is in use in the 
dairy laboratory of the Bureau of Chemistry, United 
States Department of Agriculture, the only difference 
being that the sulphuric acid u.sod is diluted with water 
until it has a specific gravity of 1 .8. 



39 



The Leach test, which is the more delicate test of the 
two, is conducted as follows: To 10 cubic centimeters of 
the milk in a porcelain evaporating dish, 10' cubic centi- 
meters of concentrated hydrochloric acid (specific gravity 
1.2) containing one part by volume of a 10 per cent ferric- 
chlorid solution per 500 parts is added and the mixture 
brought slowly to a boil over a Bunsen burner. Formalde- 
hyde is indicated by a violet coloration in intensity with 
the amount present. 

Borax and boric acid. — Twenty-five cubic centimeters of 
the milk is treated with limewater until a piece of red 
litmus paper when immersed in it turns distinctly blue. 
The mixture is evaporated to dryness in a small platinum 
or porcelain dish and then burned to an ash. A few drops 
(not too much) of concentrated hydrochloric acid are added 
to the ash, and then a few drops of water. A strip of tm'- 
meric paper is then dipped in the solution. When the tm*- 
meric paper becomes dry, it will be of a cherry-red color if 
borax or boric acid is present. The test is still more certain 
if, when the paper is moistened with an alkaline solution, 
it turns a dark-olive color. 

A test for the detection of borax or boric acid which is in 
use in the dairy laboratory of the Bureau of Chemistry, 
United States Department of Agriculture, and by which 
the ignition of the milk is avoided, is conducted as follows: 
Ten cubic centimeters of the milk is mixed with 5 cubic 
centimeters of concentrated hydrochloric acid in a porce- 
lain evaporating dish. A strip of turmeric paper about 3 
inches long is suspended in the mixture so that at least 2 
inches of the dry strip remain out of the liqmd. The dry 
portion of the paper will gradually become moist by capil- 
larity, and if borax or boric acid is present the paper will 
take on a reddish-brown tint. If only a trace of the preserv- 
ative is present, several hours may be required for this 
color to develop. A drop of ammonia water on the red 
portion will produce an olive-green color, which becomes 
lighter and finally disappears as the ammonia evaporates. 



40 



CHEMICALS AND APPARATUS USED IN THE 
CHEMICAL ANALYSIS OF MILK AND CREAM. 



Chemicals: 

Ammonia water. 

Borax or boric acid. 

Caustic soda. 

Caustic soda tenth- 
normal solution. 

Caustic potash. 

Corrosive sublimate. 

Ether. 

Ferric chlorid. 

Formaldehyde. 

Hydrochloric acid, con- 
centrated. 

Potassium bichromate. 

Phenolphthalein . 
■ Sulphuric acid, com- 
mercial. 

Sulphuric acid, pure 
concentrated. 

Litmus paper, blue. 

Litmus paper, red. 

Turmeric paper. 
Apparatus: 

Balance, analytical , 
with weights. 

Balance, cream test. 

Balance, Westphal. 

Babcock tester. 

Beakers, 250 c. c. and 
500 c. c. 

Burner, Bunsen. 

Burette, 50 c. c, gradu- 
ated to tenths, with 
stopcock. 



Apparatus — Continued . 

Cylinder, for acid hy- 
drometer. 

Cylinder, for lactome- 
ter. 

Condenser for oven. 

Desiccator. 

Dishes, milk. 

Dishes, evaporating, 
either porcelain or 
platinum. 

Drying oven, double- 
walled. 

Forceps. 

Hydrometer, acid. 

Jars, sample. 

Jars, stoneware. 

Lactometer. 

Measure, acid, 17.5 c. c. 

Pipette, 17.6 c. c. 

Pipette, 50 c. c. 

Stirring rods, glass. 

Support for biuette. 

Test bottles, Babcock, 
for milk. 

Test bottles, Babcock, 
for cream. 

Test bottles, Babcock, 
for skim milk. 

Tongs, crucible. 

Test tubes, 6 by ^ inch. 



41 



Table III. — Comparison of metric and customary weights 

and measures. 



Customary 

weights and 

measures. 



linch 

Ifoot 

1 square inch. 

1 square foot. 

1 cubic inch. . 

1 cubic foot . . 

1 fluid ounce. 

1 quart 

1 gallon 

1 grain 

1 ounce (av.) . 
1 pound (av.) 



Equivalents in 
metric system. 



2.54 centimeters. 

0.3048 meter. 

6.452 square centi- 
meters. 

9.29 square deci- 
meters. 

16.387 cubic centi- 
meters. 

0.0283 cubic meter. 

29.57 cubic centi- 
meters. 
0.9464 liter. 
3.7854 liters. 
64.8 milligrams. 
28.35 grams. 
0.4536 kilogram. 



Metric 

weights and 

measm-es. 



1 meter 

1 meter 

1 square cen- 
timeter. 

1 square me- 
ter. 

1 cubic centi- 
meter. 

1 cubic centi- 
meter. 

1 cubic deci- 
meter. 

1 liter 

1 dekaliter..., 

1 gi'am 

1 gram 

1 kilogram. ., 



Equivalents in 
customary system. 



39.37 inches. 
1.0936 yards. 
0.155 square inch. 

-10.764 square feet. 

0.061 cubic inch. 

0.0338 fluid oimce. 

61.023 cubic inches. 

1. 0567 quarts. 
2.6417 gallons. 
15.43 grains. 
0.035274 ounce. 
2.2046 pounds (av.) 



Table IV. — Comparison of Fahrenheit 
thermometer scales. 



and centigrade 



Fah- 


Centi- 


Fah- 


Centi- 


Fah- 


Centi- 


ren- 
heit. 


grade. 


heit. 


grade. 


ren- 
heit. 


grade. 





o 





o 





o 


212 


100.00 


183 


83.89 


154 


67.78 


211 


99.44 


182 


83.33 


153 


67.22 


210 


98.89 


■ 181 


82.78 


152 


66.67 


209 


98.33 


180 


82.22 


151 


66.11 


208 


97.78 


179 


81.67 


150 


65.55 


207 


97.22 


178 


81.11 


149 


65.00 


206 


96.67 


177 


80.55 


148 


64.44 . 


205 


96. 11 


176 


80.00 


147 


63.89 


204 


95.55 


175 


79.44 


146 


63.33 


203 


■ 95.00 


174 


78.89 


145 


62.78 


202 


94.44 


173 


78.33 


144 


62.22 


201 


93.89 


172 


77.78 


143 


61.67 


200 


93.33 


171 


77.22 


142 


61.11 


199 


92.78 


170 


76.67 


141 


60.55 


198 


92.22 


169 


76.11 


140 


60.00 


197 


91.67 


168 


75.55 


139 


59.44 


196 


91.11 


167 


75.00 


138 


58.89 


195 


90.55 


166 


74.44 


137 


58.33 


194 


90.00 


165 


73.89 


136 


57.78 


193 


89.44 


164 


72.33 


135 


57.22 


192 


88.89 


163 


72.78 


134 


56.67 


191 


88.33 


162 


71.22 


133 


56.11 


190 


87.78 


161 . 


71.67 


132 


55.55 


189 


87.22 


160 


71.11 


131 


55.00 


188 


86.67 


159 


70.55 


130 


54.44 


187 


86.11 


158 


70.00 


129 


53.89 


186 


85.55 


157 


69.44 


128 


53.33 


185 


85.00 


156 


68.89 


127 


52.78 


184 


84.44 


155 


68.33 


126 


52.22 



42 



Table IV. — Fahrenheit and centigrade thermometer scales- 

Continued . 



Fah- 


Centi- 


Fah- 


Centi- 


Fah- 


Centi- 


ren- 
heit. 


grade. 


ren- 
heit. 


grade. 


ren- 
heit. 


grade. 


o 


o 


o 


o 


o 


o 


125 


51.67 


82 


27.78 


39 


3.89 


124 


51.11 


81 


27.22 


38 


3.33 


123 


50.55 


80 


26.67 


37 


2.78 


122 


50.00 


79 


26.11 


36 


2.22 


121 


49.44 


78 


25.55 


35 


1.67 


120 


48.89 


77 


25.00 


34 


1.11 


119 


48.33 


76 


24.44 


33 


0.55 


118 


47.78 


75 


23.89 


32 


0.00 


117 


47.22 


74 


23.33 


31 


- 0.55 


116 


46.67 


73 


22.78 


30 


- 1.11 


115 


46.11 


72 


22.22 


29 


- 1.67 


114 


45.55 


71 


21.67 


28 


- 2.22 


113 


45.00 


70 


21.11 


27 


- 2.78 


112 


44.44 


69 


20.55 


26 


- 3.33 


111 


43.89 


68 


20.00 


25 


- 3.89 


110 


43.33 


67 


19.44 


24 


- 4.44 


109 


42.78 


66 


18.89 


23 


- 5.00 


108 


42.22 


65 


18.33 


22 


- 5.55 


107 


41.67 


64 


17.78 


21 


- 6.11 


106 


41.11 


63 


17.22 


20 


- 6.67 


•105 


40.55 


62 


16.67 


19 


- 7.22 


104 


40.00 


61 


16.11 


18 


- 7.78 


103 


39.44 


60 


15.55 


17 


- 8.33 


102 


38.89 


59 


15.00 


16 


- 8.89 


101 


38.33 


58 


14.44 


15 


- 9.44 


100 


37.78 


57 


13.89 


14 


-10.00 


99 


37.22 


56 


13.33 


13 


-10.55 


98 


36.67 


55 


12.78 


12 


-11.11 


97 


36.11 


54 


12.22 


11 


-11.67 


96 


35.55 


53 


11.67 


10 


-12. 22 


95 


35.00 


52 


11.11 


9 


-12.78 


94 


34.44 


51 


10.55 


8 


-13. 33 


93 


33.89 


50 


10.00 


7 


-13. 89 


92 


33.33 


49 


9.44 


6 


-14. 44 


91 


32.78 


48 


8.89 


5 


-15.00 


90 


32.22 


47 


8.33 


4 


-15. 55 


89 


31.67 


46 


7.78 


3 


-16.11 


88 


31.11 


45 


7.22 


2 


-16.67 


87 


30.55 


44 


6.67 


1 


-17. 22 


86 


30.00 


43 


6.11 





-17.78 


85 


29.44 


42 


5.55 


- 1 


-18.33 


84 


28.89 


41 


5.00 


- 2 


-18. 89 


83 


28.33 


40 


4.44 


- 3 


-19.44 



o 



LIBRARY OF CONGRESS 



000 895 605 4 i 




